Protocol%20Architecture

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Protocol Architecture

1. Protocols
2. Connection-Oriented and Connectionless Protocols
3. OSI Standard Architecture
4. TCP/IP Protocol Architecture
5. Vertical Communication Between Layer Processes

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1. Protocols
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Key Elements of a Protocol

• Syntax
• Data formats
• Signal levels
• Semantics
• Control information
• Error handling
• Timing
• Speed matching
• Sequencing

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Standards
Standards are rules of operation that allow two
hardware or software processes to work
together Even if they are from different vendors
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Figure 2-1 Standards Govern the Exchange of
Messages

• Standards Govern the Exchange of Messages
• Messages must be governed by strict rules
• Because computers are not intelligent

Message
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Figure 2-1 Standards Govern the Exchange of
Messages (Continued)

• Standards Govern Syntax
• Syntax the organization of the message
• Human example Susan thanked Tom
• This sentence has a subject-verb-object syntax
• Standards Govern Semantics
• Semantics The meaning of the message
• Human example Susan thanked Tom
• Humans understand this message easily

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Figure 2-1 Standards Govern the Exchange of
Messages, Continued

• General Message Syntax (Organization)
• General Message Organization (Figure 2-4)
• Primary parts of messages
• Data Field (content to be delivered)
• Header (everything before the data field)
• Trailer (everything after the data field)
• The header and trailer act like a delivery
  envelope for the data field.

Header
Data Field
Trailer
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Figure 2-1 Standards Govern the Exchange of
Messages, Continued

• General Message Syntax (Organization)
• Header and trailer are further divided into fields

Trailer
Data Field
Header
Other Header Field
Destination Address Field is Used by Switches and
Routers Like the Address on an Envelope
Message with all three parts
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Figure 2-4 General Message Organization,
Continued
Data Field
Header
Other Header Field
Destination Address Field
Message without a trailer Usually only data
link layer messages have trailers
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Figure 2-4 General Message Organization,
Continued
Header
Message with only a header e.g. TCP
supervisory messages are pure headers (there is
no data field content to deliver)
Other Header Field
Destination Address Field
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2.Connection-Oriented andConnectionless
Protocols
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Figure 2-6 Connection-Oriented and
Connectionless Protocols
Connectionless Protocol
Connection-Oriented Protocol
A
B
Message (No Sequence Number)
Message 1 (Seq. Num A1)
Connection-oriented protocols Formal openings and
closings Also have sequence numbers so that the
receiver can put messages in order And so the
receiver can send Acknowledgments for
specific messages
Close Connection
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Figure 2-6 Connection-Oriented and
Connectionless Protocols, Continued
Client PC Browser
Webserver Application
HTTP Request
HTTP is connectionless No Openings No
Closings No Sequence Numbers No Acknowledgments
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Figure 2-6 Connection-Oriented and
Connectionless Protocols, Continued
In TCP
Client PC TCP Process
Webserver TCP Process
Connection-Opening Messages
Messages During the Connection
Time
Connection-Closing Messages
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Figure 2-7 Advantages and Disadvantages or
Connection-Oriented Protocols

• Advantages
• Thanks to sequence numbers, the parties can tell
  if a message is lost.
• Error messages, such as ACKs can refer to
  specific messages.
• Long messages can be fragmented into many smaller
  messages that can fit inside packets.
• Fragmentation followed by reassembly on the
  destination host is an important concept in
  networking.

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Figure 2-7 Advantages and Disadvantages or
Connection-Oriented Protocols, Cont.

• Disadvantages
• The presence of many supervisory messages
  consumes existing bandwidth
• The processing of connection information places a
  heavy processing load on computers connected to
  the network

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3. OSI Standard Architecture
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Standards Architecture

• A Standards Architecture is a Broad Plan for
  Creating Standards
• Break the problem of effective communication into
  smaller pieces for ease of development
• Develop standards for the individual pieces
• Just as a building architect creating a general
  plan for a house before designing the individual
  rooms in detail

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OSI

• Open Systems Interconnection
• Developed by the International Organization for
  Standardization (ISO)
• Seven layers
• A theoretical system delivered too late!
• TCP/IP is the de facto standard

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OSI - The Model

• A layer model
• Each layer performs a subset of the required
  communication functions
• Each layer relies on the next lower layer to
  perform more primitive functions
• Each layer provides services to the next higher
  layer
• Changes in one layer should not require changes
  in other layers

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Why Layer?

• Breaking up large tasks into smaller tasks and
  assigning tasks to different individuals is
  common in all fields
• Specialization in standards design (EEs for
  physical layer, application specialists for
  application layer, etc.)
• Simplification in standards design for individual
  standards
• If you change a standard at one layer, you do not
  have to change standards at other layers

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OSI Layers
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The OSI Environment
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Protocol Data Units (PDU)

• At each layer, protocols are used to communicate
• Control information is added to user data at each
  layer (PDU Control Data)
• Transport layer may fragment user data
• Each fragment has a transport header added
• Destination SAP
• Sequence number
• Error detection code
• This gives a transport protocol data unit

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Protocol Data Units
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OSI as Framework for Standardization
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Figure 2.9Layer Specific Standards
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4. TCP/IP Protocol Architecture
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TCP/IP Protocol Architecture

• Developed by the US Defense Advanced Research
  Project Agency (DARPA) for its packet switched
  network (ARPANET)
• Used by the global Internet
• No official model but a working one.
• Application layer
• Transport layer
• Internet layer
• Data Link layer (Network Access)
• Physical layer

(host-to-host)
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Hybrid TCP/IP-OSI Architecture
General Purpose Layer Specific Layer Purpose
Application-application communication Application (5) Application-application interworking
Transmission across an internet Transport (4) Host-host communication
Transmission across an internet Internet (3) Packet delivery across an internet
Transmission across a single network (LAN or WAN) Data Link (2) Frame delivery across a network
Transmission across a single network (LAN or WAN) Physical (1) Device-device connection
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Figure 2-8 Hybrid TCP/IP-OSI Architecture,
Continued

• Physical and Data Link Layer Standards
• Govern Communication Through a Single Network
• LAN or WAN

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Physical Layer

• Physical interface between data transmission
  device (e.g. computer) and transmission medium or
  network
• Characteristics of transmission medium
• Signal levels
• Data rates
• etc.

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Figure 2-9 Physical and Data Link Layer
Standards in a Single Network

• Physical Layer
• Physical layer standards govern transmission
  between adjacent devices connected by a
  transmission medium

Physical Link A-X1
Switch X1
Host A
Switch X2
Physical Link X1-X2
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Figure 2-9 Physical and Data Link Layer
Standards in a Single Network, Continued

• Data Link Layer
• Data link layer standards govern the transmission
  of frames across a single networktypically by
  sending them through several switches along the
  data link

Host B
Data Link A-B
Switch X1
Host A
Switch X2
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Figure 2-9 Physical and Data Link Layer
Standards in a Single Network, Continued

• Data Link Layer
• Data link layer standards also govern
• Frame organization
• Switch operation

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Figure 2-9 Physical and Data Link Layer
Standards in a Single Network, Continued
3 Physical Links 1 Data Link 2 Switches
Host A
Switch
Data Link A-R1
Switch
Physical Link A-X1
Server Station
Switch X1
Physical Link X1-X2
Physical Link X2-R1
Switch X2
Mobile Client Station
Router R1
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Figure 2-10 Internet and Data Link Layers in an
Internet

• Internet and Transport Layers
• An internet is a group of networks connected by
  routers so that any application on any host on
  any network can communicate with any application
  on any other host on any other network
• Internet and transport layer standards govern
  communication across an internet composed of two
  or more single networks

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Figure 2-10 Internet and Data Link Layers in an
Internet, Continued

• Internet Layer
• Internet layer standards govern the transmission
  of packets across an internettypically by
  sending them through several routers along the
  route
• Messages at the internet layer are called packets
• Internet layer standards also govern packet
  organization and router operation

Router 1
Router 2
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Figure 2-10 Internet and Data Link Layers in an
Internet, Continued
Host A
Data Link A-R1
R1
Network X
Network Y
3 Data Links One per Network 1 Route per Internet
Data Link R1-R2
Route A-B
Network Z
R2
Host B
Data Link R3-B
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Figure 2-10 Internet and Data Link Layers in an
Internet, Continued
Frame X
Packet
Data Link A-R1
Switch
In Network X Two Destination Addresses Packet
Host B (Destination Host) Frame Router R1
Host A
Switch
Server Station
Switch X1
Mobile Client Station
Switch X2
Route A-B
Router R1
Network X
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Figure 2-10 Internet and Data Link Layers in an
Internet, Continued
To Network X
Route A-B
Router R1
Frame Y
Data Link R1-R2
In Network Y Two Destination Addresses Packet
Host B (Destination Host) Frame Router R2
Packet
Router R2
To Network Z
Network Y
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Figure 2-10 Internet and Data Link Layers in an
Internet, Continued
Frame Z
Packet
Data Link R2-B
Switch Z1
Host B
Router R2
In Network Z Two Destination Addresses Packet
Host B (Destination Host) Frame Host B
Switch Z2
Mobile Client Stations
Switch X2
Router
Network Z
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Frames and Packets

• In an internet with hosts separated by N
  networks, there will be
• 2 hosts
• One packet (going all the way between hosts)
• One route (between the two hosts)
• N frames (one in each network)
• N-1 routers (change frames between each pair of
  networks)
• There usually are many switches within single
  networks
• There usually are many physical links within
  networks

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Figure 2-11 Internet and Transport Layer
Standards

• Transport Layer
• Transport layer standards govern aspects of
  end-to-end communication between two end hosts
  that are not handled by the internet layer
• These standards allow hosts to work together even
  if the two computers are from different vendors
  and have different internal designs

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Figure 2-11 Internet and Transport Layer
Standards, Continued
Transport Layer end-to-end (host-to-host) TCP is
connection-oriented, reliable UDP is
connectionless and unreliable
Server
Client PC
Internet Layer (usually IP) hop-by-hop
(host-router or router-router) connectionless,
unreliable
Router 1
Router 2
Router 3
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Figure 2-12 Application Layer Standards

• Application Layer
• The application layer governs how two
  applications work with each other, even if they
  are from different vendors

Browser
Webserver Application
Webserver
Client PC
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Figure 2-12 Application Layer Standards

• There are more application layer standards than
  any other type of standard because there are many
  applications
• HTTP
• E-Mail
• Database
• Instant Messaging
• FTP
• Etc.

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Some Protocols in TCP/IP Suite
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5.Vertical Communication Between Layer Processes
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Figure 2-18 Layered Communication on the Source
Host
The process begins when a browser creates an HTTP
request message
Application Process
HTTP Message
Passes Message Down to Transport Process
Transport Process
HTTP Message
TCP Hdr
Encapsulation of HTTP Message in Data Field of
TCP Segment
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Figure 2-18 Layered Communication on the Source
Host, Continued

• When a layer process (N) creates a message, it
  passes it down to the next-lower-layer process
  (N-1) immediately
• The receiving process (N-1) will encapsulate the
  Layer N message, that is, place it in the data
  field of its own (N-1) message

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Figure 2-18 Layered Communication on the Source
Host, Continued
Transport Process
HTTP Message
TCP Hdr
Internet Process
HTTP Message
TCP Hdr
IP Hdr
Encapsulation of TCP Segment in Data Field of IP
Packet
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Figure 2-18 Layered Communication on the Source
Host, Continued
Internet Process
HTTP Message
TCP Hdr
IP Hdr
Data Link Process
HTTP Message
TCP Hdr
IP Hdr
Eth Hdr
Eth Trlr
Encapsulation of IP Packet in Data Field of
Ethernet Frame
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Figure 2-18 Layered Communication on the Source
Host, Continued
Data Link Process
HTTP Message
TCP Hdr
IP Hdr
Eth Hdr
Eth Trlr
Physical Process
Physical Layer converts the bits of the frame
into signals.
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Figure 2-18 Layered Communication on the Source
Host, Continued
The following is the final frame for a an HTTP
message on an Ethernet LAN
HTTP Message
TCP Hdr
IP Hdr
Eth Hdr
Eth Trlr
L5
L4
L3
L2
L2
Notice the Pattern From Right to Left L2, L3,
L4, L5, maybe L2 This makes it easier to remember
the order of headers and messages Dont forget
the possible trailing L2 trailer
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Figure 2-19 Decapsulation on the Destination Host
HTTP Message
TCP Hdr
IP Hdr
Eth Hdr
Eth Trlr
Data Link Process
Physical Process
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Figure 2-19 Decapsulation on the Destination
Host, Continued
Internet Process
HTTP Message
TCP Hdr
IP Hdr
HTTP Message
TCP Hdr
IP Hdr
Eth Hdr
Eth Trlr
Data Link Process
Decapsulation of IP Packet from Data Field of
Ethernet Frame
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Figure 2-19 Decapsulation on the Destination
Host, Continued
Transport Process
HTTP Message
TCP Hdr
Internet Process
HTTP Message
TCP Hdr
IP Hdr
Decapsulation of TCP Segment from Data Field of
IP Packet
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Figure 2-19 Decapsulation on the Destination
Host, Continued
Application Process
HTTP Message
Transport Process
HTTP Message
TCP Hdr
Decapsulation of HTTP Message from Data Field of
TCP Segment
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PDUs in TCP/IP
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Figure 2-20 Layered End-to-End Communication
Routers Have Three Layers --- Each
Router Port Has Two Layers (12)
Switches Have Two Layers --- Each Switch Port Has
One Layer (1)
Source and Destination Hosts Have 5 Layers
Source Host
Destination Host
Switch 1
Switch 2
Router 1
Switch 3
Router 2
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Figure 2-21 Combining Horizontal and Vertical
Communication
Hypertext Transfer Protocol
Transmission Control Protocol
Internet Protocol
Destination Host
Source Host
Switch 2
Router 1
Switch 3
Router 2
Switch 1
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Telnet Data
TCP Header Telnet Data
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IP Header TCP Header Telnet Data
Ethernet Frame Header IP Header TCP Header
Telnet Data
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Example Header Information

• Destination port
• Sequence number
• Checksum

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Figure 2-23 OSI and TCP/IP
OSI
TCP/IP
Standards Agency or Agencies
ISO (International Organization for
Standardization) ITU-T (International Telecommun
ications Union Telecommunications Standards
Sector)
IETF (Internet Engineering Task Force)
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Figure 2-23 OSI and TCP/IP, Continued
OSI
TCP/IP
Dominance
Nearly 100 dominant at physical and data link
layers
70-80 dominant at the internet and
transport layers.
Documents are Called
Various
Mostly RFCs (requests for comments)
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Figure 2-26 Characteristics of Protocols
Discussed in the Chapter
Layer
Protocol
Connection- Oriented /Connectionless
Reliable/ Unreliable
5 (App)
HTTP
Connectionless
Unreliable
4 (Transport)
TCP
Connection- oriented
Reliable
4 (Transport)
UDP
Connectionless
Unreliable
3 (Internet)
IP
Connectionless
Unreliable
2 (Data Link)
Ethernet
Connectionless
Unreliable
Note Only TCP is connection-oriented and reliable